With the explosive spread of data communication networks such as the Internet, there are increasing needs for expanding the capacity of optical communication networks. To meet such growing network demands, wavelength-division multiplexing is in practical use, and in recent years, there have also been growing demands for wavelength selective switching (WSS), which enables route switching of optical signals on a per-wavelength basis without converting the optical signals into electrical signals. The node configuration using wavelength selective switching is called a reconfigurable optical add/drop multiplexing (ROADM) system.
Recently, a node configuration called multi-degree ROADM (see NPL 1) that processes optical signals from various routes has particularly been researched and developed actively, and multi-degree ROADM is beginning to be used in actual communication systems.
A large number of optical signals may be dropped at nodes of such systems, and to process such signals, a configuration which employs multicast switching as a transponder aggregator (TPA) has been designed. A transponder aggregator may connect optical signals from given routes to given transponders.